1. Field of the Invention
The present invention relates to rotating magnetic disk drives, and more particularly, to a method for iteratively determining repeatable runout written to a servo track during a servowriting process for accurate track following relative to a concentric track center.
2. Description of the Prior Art and Related Information
Repeatable runout (RRO) in a disk drive results from imperfections, with respect to a perfect circle, in the location of servo information along a track on a disk surface in the disk drive. Due to disk spindle rotation, the servo imperfections due to RRO are periodic having a fundamental frequency that is equal to the spindle rotation frequency. The RRO imperfections are relatively static over time and the effect of the RRO may be attenuated by measuring the RRO during manufacturing and using the RRO measurements in a head-position servo loop to compensate for the RRO effect.
U.S. Pat. No. 6,563,663 discloses a scheme for determining RRO compensation values using Iterative Learning Control (ILC) based on an update law having a digital filter. However, acceptable RRO compensation values are obtained after numerous disk rotations using the digital filter based ILC and update law. The numerous disk rotations unfortunately impact disk drive manufacturing throughput.
Accordingly, there exists a need for a technique for iteratively determining RRO cancellation values in a disk drive without unnecessarily increasing manufacturing costs or significantly impacting manufacturing throughput. The present invention satisfies these needs.